1. Field of the Invention
The invention discloses reinforced co-tapered, variable stiffness tubing, and more specifically a reinforced tubing using an encapsulated braid.
2. Brief Description of the Prior Art
Catheterization procedures are used to diagnose the condition of a patient's body tissue such as arterial passageways or the like. Normally, an incision is made in the patient's body in order to insert the catheter apparatus into the passageways to be diagnosed. The catheter is then inserted through the incision and into the desired passageway. The catheter is fed through the passageway until it is correctly positioned adjacent the desired body organ, such as the heart. The catheter is then precisely rotated and manipulated into the desired body organ, for instance, the right coronary artery. Diagnostic fluid is then injected into the passageway at a predetermined minimum flow rate in order for a separate device, such as an x-ray; to properly record in photograph form the condition of the passageway.
Dilatation catheters predominately fall into two categories, over-the-wire catheters that are fed over a guide wire and fixed wire catheters, which serve as their own guide wire. Wireless dilatation balloon catheters have been developed in an attempt to obtain some of the advantage of an over-the-wire catheter. Dilatation catheters must offer flexibility to allow the catheter to maneuver through tight curvatures in the vascular system. The physician must also have the ability to transmit longitudinal force, from the proximal to the distal ends, to push the catheter through the guide catheter and arteries and across the stenosis.
Angioplasty is an effective method of opening stenosis in the vascular system. In the most commonly used form of angioplasty, a balloon catheter is guided through the vascular system in position across the stenosis. Once in position, the balloon is inflated, the artery opened and acceptable blood flow reestablished.
The above procedures, however, frequently induce trauma to the walls of the patient's passageways. Prior art catheters have sought to reduce this trauma by providing a highly flexible catheter that bends in conformance with the passageways. In order to allow the catheter to be fed through the passageways, the catheter must have sufficient rigidity to provide adequate torque transmission. Without sufficient torque transmission, the catheter cannot be precisely rotated into the desired body organ. Further, poor torque transmission causes buckling, wind-up and whiplash, inducing trauma to the passageways and causing pain and discomfort to the patient.
Thus, the medical profession has been faced with a trade-off between a highly flexible catheter apparatus that fails to function adequately when in torsion or a rigid catheter that creates an intolerable amount of trauma.
U.S. Pat. No. 5,805,649 issued to Flynn, discloses a Torque Controlled Tube that utilizes the co-tapering of polymeric materials, such as polyamides and polyurethanes, to produce a tube that is variable in stiffness. While this construction produces adequate pushability and kink resistance results for thick walled tubing, it does not address problems inherent in thin-walled tubing. The stiffer material is in higher concentration in the sections(s) of the tube that requires good pushability while the softer material is in higher concentration in the tube sections that require greater flexibility.
To address problems associated with thin walled tubing, many angiography and guiding catheters are constructed by encapsulating a braid for added strength and flex properties. Unfortunately, due to the construction methods of these catheters, the braid pattern remains constant throughout the entire length of the catheter, with exception of the tip region, therefore compromising performance characteristics through out the different segments of the catheter.
One method of producing a variable stiffness tube, suitable for medical device applications, is disclosed in U.S. Pat. No. 5,531,721, Multiple Member Intravascular Guide Catheter. This patent relates to the bonding/joining of multiple tube sections. These tube sections may or may not be reinforced. The difficulty in producing a catheter of this nature is that the transition from a "stiff" section to a "soft" section is not achieved continuously. Rather at each joint, a stress riser may occur that can weaken the tube's structure thereby leading to possible premature kinking when flexed or rupturing when pressurized.
Engleson, U.S. Pat. No. 5,312,356, discloses a Catheter with Low-Friction Distal Segment that utilizes a variable braided pattern to minimize jamming, stick or locking of the distal end of the catheter or any part of the guide wire against the surface. The braided material is exposed on the inner surface of the tube at the distal tip of this catheter and is not used to provide variable stiffness but rather as a means of preventing the sticking problems mentioned previously.
Many other patents have addressed the problem of minimizing body trauma during insertion of a catheter. These include the use of a glass transition material (U.S. Pat. No. 5,441,489 to Utsumi et al); a single-lumen shaft for use with either a fixed-wire balloon catheter or an innerless catheter (U.S. Pat. No. 5,533,987 to Pray et al); and a collapsible shaft and guide wire lumen (U.S. Pat. No. 5,466,222 to Ressemann et al). Muni et al (U.S. Pat. No. 5,569,196) discloses a tractable catheter having two lumens that vary in Shore hardness. In U.S. Pat. No. 5,603,705 to Berg, an intravascular catheter is constructed with an outer layer and an inner layer that is covered with a support surface, such as a stainless steel wire braid. Another dual lumen catheter that includes a wire braid between the two lumens, is disclosed in U.S. Pat. No. 5,078,702 to Pomeranz. In U.S. Pat. No. 5,254,107 to Soltesz the plastic catheter shaft has embedded the braid within the outer catheter shaft. In U.S. Pat. No. 4,764,324 to Burnham also incorporates the reinforcing member into the outer lumen by heating the lumen after molding. U.S. Pat. No. 5,221,270 to Parker discloses the use of tapered ends on the catheter materials to change from a harder Shore to a softer Shore and provide an outer diameter with a uniform, continuous outer layer.
U.S. Pat. No. 4,425,919 has sought to overcome the foregoing problems by providing a catheter with a small outside diameter and utilizing a pre-oriented substrate that adequately supports the reinforcing means. A flat braid is used which is maintained in its position around the substrate by a surrounding superstrate.